Pearls as small as 100 to a diamond carat are drilled and used in seed-pearl work. Diamonds, rubies, and even sapphires, however, are cut in brilliant form when they are as small as 250 to 300 to the carat, or 45,000 to the ounce. The price of these small pearls, however, is only from eight to fifteen cents per carat, whereas diamonds of this size are worth from $200 to $300, their value being three times that of those weighing one sixteenth to one eighth carat each. This is due to the fact that the labor expended in cutting the smaller diamonds is much greater than that bestowed upon the pearls, which simply require drilling and not cutting.
“Half-pearl,” as we have mentioned, is the name given to such pearls as are round and spherically domed and are either somewhat flat or almost the shape of one half of a whole pearl of the same diameter. They are produced in two ways: some are cut away as hemispheres from the inner surface of the shell of the pearl-mussel, but more usually they are the better portions of defective whole pearls which are sawn or split by hand into two “halves” with a minute saw, the defective part being rejected altogether or classified as inferior half-pearl, while the better half is classified as a I or II quality half-pearl. Frequently a fine specimen is obtained from an elongated pearl, and sometimes two, three, or even four half-pearls are secured from the various bright parts of a round pearl. In splitting half-pearls, the pearl to be operated upon is held by hand in a kind of grooved vice or pincers and sawn through with a very fine saw; this process is at once simple, rapid, and of insignificant cost.
Only pearls which cannot be cut are filed. In this process the poorer side of the pearl in question is laid upon the file, and the operator takes a piece of ordinary hard wood, so formed that he can grasp it firmly in his hand, presses it down upon the pearl, and rubs the latter on the file, removing all but the good side. In this way a half-pearl is produced.
The smaller half-pearls are from .5 to .75 millimeters in diameter, and an ordinary ounce of half-pearl material will number 18,000. Of the manufactured half-pearls there are, on an average, 20,528 to an ounce.
The half-pearl industry is largely carried on in Idar, on the Nahe River, and in Oberstein, in the Duchy of Oldenburg, Germany. The pearls are usually purchased from London or Paris houses in lots valued up to $12,000 or more, although some of the firms buy directly from India. In Idar about one hundred people are employed in this industry. Frequently it is pursued m the home of the manufacturer, who may employ from one to a dozen or more workers. These generally include a sorter or arranger, and a marker to indicate the part of the pearl which should be sawn off. There is also a trimmer or one who finally adjusts the pearls.
An unusually clever bit of deception was practised by an American pearl fisher who had found two pearl blisters of almost identical size. Both of these blisters were hollow, and were alike in form. The pearl dealer very cleverly polished down both sides, rounded off the edges, cemented the two backs together, and except for a tiny edge they had all the appearance of a drop pearl that was fairly perfect on both sides. It required but a little heating to separate the parts and show the deception.
In setting half-pearls, they are generally selected from large lots with great care as to their being of uniform size. A circular place for the setting is often drilled with a steel drill, either for several or for a single one. The half-pearl is frequently placed on one or more tiny disks of paper, to give it the exact height in the setting, and the edge of gold is rubbed up against the pearl, which is thus secured in its place; or else tiny edges of gold are left projecting between each pearl. These are pressed down after the pearl is in place. This process requires great delicacy and skill and is frequently employed in the decoration of pearl lockets and watches. In some of the cheaper work, the half-pearls are cemented into the shallow disks that were drilled for them, but frequently they are secured by metal points skilfully raised out of the disks in which the pearls are set, and then pressed down to hold the latter in place. Although apparently frailly set, it is surprising that half-pearl ornaments have been owned for more than a century, scarcely a pearl dropping out; and even if one or two pearls should be lost from the piece of jewelry, the expense of replacing them is not very great. They are often not as safely set when they are mounted with diamonds, rubies, or other stones, more especially in rounded rings or bracelets.
In drilling gold for the setting of half-pearls, where the hole must not be carried right through the metal, a so-called “pearl drill” is used. This is designed to cut a hole with a flat base in comparatively thin layers of metal without disfiguring the opposite side, a task that can easily be accomplished if care be taken not to drill deeper than is strictly necessary for the safe adjustment of the pearl. For the construction of this drill a piece of round steel wire of suitable size is chosen; this is hammered flat at one end and then filed away at each side, leaving a small spike standing in the center, which projects a little beyond the cutting edges and acts as a pivot on which the drill revolves. The steel on both sides of this spike is filed down to a fine edge, care being taken to preserve the horizontal line, so that when the spike is embedded in the metal both cutting edges come into play simultaneously. If the drill is in good condition, it does its work very rapidly, since it is used in an upright drill-stock, whose weight gives a uniform and constant pressure. A good range of sizes of this drill should be kept ready for use, so that one may be found to suit the dimensions of any given pearl. This is essential in order to make an opening just large enough to hold the gem, so that it may fit tightly, without the necessity of reaming out the hole.
Half-pearls were frequently used with the most pleasing effect in the decoration of antique watches. A number of remarkable examples of this type are among the collection of antique watches of Henry Walters of Baltimore. This collection had been acquired by Tiffany & Co. after the sale of the San Donato Palace, the watches having been withdrawn from the prince’s collection by his sister sometime before the sale.
In mounting pearls on gold, a white paste is sometimes employed in half-pearl mounting, which is called by the French jewelers gouache. This substance contains white lead, and its use is liable to be injurious to the workmen, cases of lead colic having been recently recognized as thus produced. This subject has lately (1907) been brought forward at the Société Médicale des Hôpitaux in Paris. The cases were at first mistaken for appendicitis, but proved to be well-marked cases of lead poisoning. They had not been reported previously, and are evidently not frequent, those noted being confined to instances in which the employees had carelessly been in the habit of removing an excess of the paste with the tongue.